1. Field of the Invention
The present invention relates to computer systems, and more particularly, to a bus arbitration system suitable a variety of input and output devices of different characteristics.
2. Discussion of the Related Art
A conventional bus arbitration system will be described with reference to the accompanying drawings.
FIG. 1 shows a conventional bus arbitration system according to daisy-chain mode.
As illustrated in FIG. 1, the conventional bus arbitration system according to daisy-chain mode includes a plurality of arbiters connected to one another in series with a sequential priority order, and a bus busy line connected to the respective arbiters.
Output terminals PO of the respective arbiters are respectively connected to input terminals PI of their successive arbiters. The respective arbiters are connected to a bus line.
Such a bus arbitration system allows the respective arbiters to use the bus line sequentially. In other words, the bus arbitration system allows a first arbiter to use the bus line firstly and also allows the last arbiter to use the same lastly. The bus arbitration system allows the arbiter at the next level to use the bus line if the first arbiter does not request to use the same.
In this respect, if any one of a plurality of the arbiters has an input value "1" and does not request to use the bus line (that is, if it does not request interrupt), it has an output value "1". The output value "1" is transferred to the input terminal of the successive arbiter.
Meanwhile, if any one of a plurality of the arbiters has an input value "1" and requests to use the bus line, it has an output value "0" and has the priority capable of using the bus line. Then, the arbiter recognizes the bus busy line. If the other device uses the bus line, the arbiter uses the bus line after the other device completed its use. If the other device does not use the bus line, the arbiter can directly use the same.
At this time, the arbiter which once had the priority has the last priority order.
Other conventional bus arbitration system which adopts round-robin mode will be described with reference to FIG. 2.
Referring to FIG. 2, a plurality of priority request signals (request signals for use of a bus line) are separately input to a first logic gate 21 and a second logic gate 22. The priority request signals passed through the first and second logic gates 21 and 22 are connected to a first round-robin arbiter 23. Here, the priority request signals from the first logic gate 21 are separately input to third and fourth logic gates 24 and 25, and the priority request signals from the second logic gate 22 are separately input to fifth and sixth logic gates 26 and 27.
Output signals of the third and fourth logic gates 24 and 25 are connected to a second round-robin arbiter 28, and output signals of the fifth and sixth logic gates 26 and 27 are connected to a third round-robin arbiter 29. At this time, output signals of the third round-robin arbiter 29 act as enable signals of the second and third round-robin arbiters 28 and 29.
The priority is determined by a first level corresponding to the first round-robin arbiter 23 and a second level corresponding to the second and third round-robin arbiters 28 and 29. The priority of the second level is determined as below.
Two adjacent request signals of a plurality of the priority request signals are respectively input to fourth, fifth, sixth and seventh round-robin arbiters 30, 30a, 30b and 30c.
The fourth, fifth, sixth and seventh round-robin arbiters 30, 30a, 30b and 30c at the last level are half of the input priority request signals. The fourth, fifth, sixth and seventh round-robin arbiters 30, 30a, 30b and 30c selectively output a final priority request signal.
Such a bus arbitration system of round-robin mode evenly gives the respective devices the priority.
The conventional bus arbitration systems as aforementioned have several problems.
A plurality of the devices connected to the bus line have different characteristics. For example, any one of a plurality of the devices tends to use the bus line frequently or urgently as compared to the other devices. In this case, it is difficult for the respective devices to use the bus line to be suitable for their characteristics because the priority is evenly given to all of the devices.